The present invention relates to flue-gas desulfurization equipment (hereinafter, FGD equipment) for removing sulfur dioxide from gas exhausted from factories or electrical power plants, especially to a FGD equipment which can reduce slurry circulating volume and draft pressure loss leading to energy consumption, which has approximately 100% of desulfurization rate by assuming a case of installing it as a preceding step of a device for recovering carbon dioxide gas which is installed sometime in the future and which can make byproducts gypsum at approximately 100%.
In the past, the FGD equipment removing sulfur dioxide gas from processed gas by flowing adsorbent slurry down in vertical direction in a cylindrical casing and by flowing the processed gas therein is known.
Especially in Japan, the FGD equipment whose system uses a vertical type of a cylindrical body and makes the processed gas flown vertically is used widely.
However, in the FGD equipment whose system uses the vertical type of the cylindrical body, there is problem such that energy consumption becomes large as slurry circulating volume is increased. Concretely, in the FGD equipment, since gas throughput is increased with the square of a diameter of the cylindrical body, the circulating volume of the slurry being absorbent is increased with the square of the diameter of the cylindrical body.
On the other hand, though an exhaust desulfurizer whose system is to flow the processed gas in horizontal direction by using a horizontally cylindrical body arranged so as for a rotation shaft to extend in horizontal direction is similar to the FGD equipment using the vertically cylindrical body in point that the gas throughput is increased with the square of the diameter of the cylindrical body, the slurry circulating volume is increased only in direct proportion to the diameter of the cylindrical body.
Accordingly, without pausing to image a linear expression graph and a quadratic expression graph, because the slurry circulating volume in the case of using horizontally cylindrical body is less than one in the case of using vertically cylindrical body and the energy consumption is less, so that it is advantageous to use the horizontally cylindrical body. Especially in a large type of the FGD equipment, as a cylindrical body becomes larger, it is remarkably advantageous to use the horizontally cylindrical body rather than to use the vertically cylindrical body.
Besides, the reason that the FGD equipments using the vertically cylindrical body are used widely in Japan is thought to be due to applying attitude of a gas adsorption device developing based on an original small size device to the FGD equipment being a large size device.
For instance, what are shown in Japanese utility model publication No. sho 53-19171 and Japanese patent No. 4418987 (U.S. Pat. No. 7,527,679B2/CN 101099922B) are known as the FGD equipment using the horizontally cylindrical body.
Japanese utility model publication No. sho 53-19171 is that a lot of lifters or troughs consisting of U-shaped tubs for scooping up desulfurizing agent are provided in parallel to axial direction on an inner wall of a rotation cylinder with an annular end plate having a processed gas inlet port at one end thereof and an annular end plate having an outlet port at the other end thereof, and the rotation cylinder in which a lot of separated fillers having apertures or holes are filled in a whole internal space is arranged horizontally and rotatably, and a means for supplying absorption slurry is provided at one end of the rotation cylinder and an outlet of the slurry is discharged at the other end of the rotation cylinder.
In this FGD equipment, while the fillers positioned at a lower part are immersed in the slurry retained below of the rotation cylinder, the rotation cylinder is rotated so as to bring the processed gas into contact with the absorption slurry in countercurrent flow or in parallel flow, so that gas-liquid contact can be achieved.
As an actual achievement of working the FGD equipment described in Japanese utility model publication No. sho 53-19171, there are a prototype machine with 1 m diameter of the rotation cylinder (a rotation packed bed), a first practical machine with 3.2 m diameter of the rotation cylinder, a second practical machine with 4.5 m diameter of the rotation cylinder and a third practical machine with 4.5 m diameter of the rotation cylinder, and all of them are successful, and especially the first and the second practical machine have approximately 40 years operation performance. Here, they have 3 m length in axial direction of the rotation cylinder. Besides, if considering that byproducts are calcium sulfite, the length of the rotation cylinder can be made shorter (approximately by 1 m).
The succession of these machines is to support the above opinion such that “it is remarkably advantageous to use the horizontally cylindrical body rather than to use the vertically cylindrical body in the FGD equipment being a large device”.
The operation performance of every machine is shown in Table 1:
TABLE 1GasSlurryThroughputDiameterLengthCirculating(Nm3/h)(m)(m)Volume (m3/h)Prototype Machine5,00013150First Practical60,0003.23480MachineSecond Practical90,0004.53675MachineThird Practical90,0004.53675Machine
As shown in Table 1, the slurry circulating volume is increased only in direct proportion to the diameter of the cylindrical body in each machine, it is understood that “it is remarkably advantageous to use the horizontally cylindrical body rather than to use the vertically cylindrical body in the FGD equipment being a large device”.
Thus, in the FGD equipment described in Japanese utility model publication No. sho 53-19171, about the slurry circulating volume, it should be noted that circulating volume of the slurry must be considered in proportion to the diameter of the rotation cylinder.
Furthermore, as shown in Table 1, every machine has 3 m length in the axial direction of the rotation cylinder (the rotation packed bed), and this shows it is advantageous to use the horizontal cylinder rather than to use the vertical cylinder in the case that the diameter of rotation cylinder becomes more than 3 m.
Here, it is another factor that should not be overlooked that the larger the diameter of the rotation cylinder, the larger the dropping height of the slurry in proportion to the diameter of the rotation cylinder. Namely, chemical reaction quantity associated with once dropping of the slurry is 3.2 times in the case of 3.2 m diameter of the rotation cylinder, and 4.5 times in the case of 4.5 m diameter of the rotation cylinder, based on the case of 1 m diameter of the rotation cylinder. Accordingly, in the case of a fourth trial designed machine as will become apparent below, as the diameter of the rotation cylinder is 24.3 m, the chemical reaction quantity associated with once dropping of the slurry becomes 24.3 times.
This may be thought for it to be a root that it is advantageous to flow the gas horizontally rather than to flow the gas vertically.
On the other hand, operation of the FGD equipment described in Japanese utility model publication No. sho 53-19171 is, in an aspect of chemical reaction, to produce gypsum as a byproduct by using limestone slurry as an absorbent for sulfur dioxide. In this case, process such that calcium sulfite is produced as a medium product, and then, the calcium sulfite is oxidized by oxygen in the processed gas (exhaust gas) to be gypsum is carried out.
For the process for gypsumization of the calcium sulfite, it was known that there is delicate relation between oxygen concentration in the processed gas and pH of the gypsum slurry discharged from the device.
Arranging knowledge about the process of gypsumization of the calcium sulfite as mentioned above, it is considered as follows.SO2+H2O→H2SO3  (1)CaCO3→Ca2++CO32−  (2)Ca2++H2SO3→CaSO3+2H+ (aqueous calcium sulfite)  (3)CO32−→CO2+½O2  (4)CaSO3+½H2O→CaSO3.1/2H2O (crystalline calcium sulfite)  (5)CaSO3+½O2+2H2O→CaSO4.2H2O (gypsum crystal)  (6)
In acid slurry in a slurry outlet side (a gas introducing inlet side), crystalline calcium sulfite is dissolved, and reaction shown in the following formula (7) is undergone.CaSO3.1/2H2O→CaSO3+½H2O  (7)
Furthermore, reaction shown in the following formula (8) is undergone by reacting with ½ O2 in the above formula (4) and O2 of excess air in the processed gas.CaSO3+½O2+H2O→CaSO4.2H2O  (8)
Besides, a desulfurizer for harmful gas described in Japanese Patent No. 4418987 is provided with installation of a basket-shaped rotation cylinder which is supported rotatably around a horizontal shaft in a fixed duct and inside of which gas-liquid contact fillers is filled, a slurry storage tank located below of the basket-shaped rotation cylinder, and a back-flow means for pumping up absorbent slurry in the slurry storage tank and flowing back it to an outer peripheral surface of the basket-shaped rotation cylinder. In the desulfurizer for harmful gas, since the basket-shaped rotation cylinder can be rotated only by flowing the absorbent slurry back, an electrical driving means for the basket-shaped rotation cylinder can be unneeded, it is possible to minimize the device and to reduce electrical consumption.
Recently, it is said that carbon dioxide gas that causes global heating because of smoke exhausted from factories or power plants must be recovered. And, as a previous step of recovering the carbon dioxide gas from the exhaust smoke, though a FGD equipment for removing sulfur dioxide from the exhaust smoke is used, not only low-cost but also high-performance (approximately 100% desulfurization) is required.
Furthermore, Japanese Patent No. 4505041 by the present inventors is shown as a patent invention in relation with it.